1. Field of the Invention
The present invention relates to a power supply, and more especially to a power supply which may change plug elements for matching different specifications of electrical sockets.
2. Description of the Related Art
At present, small, portable power supplies have been applied widely in people's life. Some of them are adapted to provide operational power and some of them serve as charging devices. Although these power supplies have brought people so much convenience, there are many drawbacks when people use these power supplies in different regions, since the shape and structure of electrical sockets in a region vary from those in another region.
Basically, electrical sockets are formed in four types of structure, that is BS socket with three rectangular jacks, UL socket with two tabular jacks, VDE socket with two circular jacks and SAA socket with two tabular jacks being at an angle of 60 degrees to each other. To match various sockets with different structures, people have invented many kinds of power supplies. One such device is disclosed in a Chinese patent with a publication number of CN 2304206Y which describes a traveling power supply with a changeable plug element. As shown in FIG. 1, this power supply forms an opening in its bottom cover and a movable fastener, a positioning slide sheet, a slide base, an internal base and two conduction sheets that are arranged in the opening so as to achieve the function of conduction and plug element conversion. This power supply can replace different types of plug elements in structure. However, when analyzed on the basis of security, there is an obvious hidden danger. For instance, in practice, once a situation of imprecise assembly or improper use occurs, the power plug element 14 is prone to depart from the bottom cover 11. If the power plug element 14 is still being inserted in the socket at this time, users who touch the exposed tab 144 carelessly may easily suffer an electric shock since the exposed tab 144 has the same potential as the power plug element.
A traveling power supply with a changeable plug element is disclosed in the publication number CN 2304206Y. In addition, an adapter with changeable connectors is disclosed in the patent publication number CN 2517145Y and achieves the function of plug element conversion far better and reduces the opportunity for users to contact the tab through setting a slide groove in the external cover. However, this universal adapter also has certain problems. As shown in FIG. 2, to achieve the function of the slide groove, the adapter forms openings in the upper cover and the bottom cover respectively, which make the structure too complicated to assemble. When replacing the plug element, it is only dependent on exerting the horizontal controlling force to push and pull the connector, which can cause unreliable engagement after repetitious operation. Furthermore, the connecter becomes flexible when engage with the covers. Thus, users may be in danger of getting an electric shock when touching the elements within the covers. Additionally, the circuit board is electrically connected with the plug element merely through the contact sheet 331. Because of this tenuous connection, after long-term use, the adapter may provide a poor contact.
Compared with the adapter with changeable connectors in the publication number CN 2517145Y, a multi-function conversion plug element for power supplies disclosed in the patent publication number CN 2361023Y has an improved structure which is more compact and provides for engagement between a connector and the covers in a more reliable manner. As shown in FIG. 3, the plug element only forms a slide groove in a rear cover. Between a pin element and the rear cover is located an elastic fastener 16 and a hook 160 used to fasten the plug element tightly and avoid escape of the plug from the adapter. Although this multi-function conversion plug element for power supplies has an improved structure and engagement mechanism, the poor contact between the circuit board and the pin element still exists after long-term use. In addition, its contact tab is protected by a flute 24. However, if certain conductors such as metal threads drop off into the flute 24, users may be in danger of getting an electric shock when contacting the metal threads.
Thus, it would be a distinct advantage to have a power supply with a changeable plug which is both safe to operate and resilient to continuous use. It is an object of the present invention to provide such an apparatus.